In the space of just one week last month, according to Crif, the umbrella group for France’s Jewish organisations, eight synagogues were attacked. One, in the Paris suburb of Sarcelles, was firebombed by a 400-strong mob. A kosher supermarket and pharmacy were smashed and looted; the crowd’s chants and banners included “Death to Jews” and “Slit Jews’ throats”. That same weekend, in the Barbes neighbourhood of the capital, stone-throwing protesters burned Israeli flags: “Israhell”, read one banner.

In Germany last month, molotov cocktails were lobbed into the Bergische synagogue in Wuppertal – previously destroyed on Kristallnacht – and a Berlin imam, Abu Bilal Ismail, called on Allah to “destroy the Zionist Jews … Count them and kill them, to the very last one.” Bottles were thrown through the window of an antisemitism campaigner in Frankfurt; an elderly Jewish man was beaten up at a pro-Israel rally in Hamburg; an Orthodox Jewish teenager punched in the face in Berlin. In several cities, chants at pro-Palestinian protests compared Israel’s actions to the Holocaust; other notable slogans included: “Jew, coward pig, come out and fight alone,” and “Hamas, Hamas, Jews to the gas.”

Across Europe, the conflict in Gaza is breathing new life into some very old, and very ugly, demons. This is not unusual; police and Jewish civil rights organisations have long observed a noticeable spike in antisemitic incidents each time the Israeli-Palestinian conflict flares. During the three weeks of Israel’s Operation Cast Lead in late 2008 and early 2009, France recorded 66 antisemitic incidents, including attacks on Jewish-owned restaurants and synagogues and a sharp increase in anti-Jewish graffiti.But according to academics and Jewish leaders, this time it is different. More than simply a reaction to the conflict, they say, the threats, hate speech and violent attacks feel like the expression of a much deeper and more widespread antisemitism, fuelled by a wide range of factors, that has been growing now for more than a decade.

“These are the worst times since the Nazi era,” Dieter Graumann, president of Germany’s Central Council of Jews, told the Guardian. “On the streets, you hear things like ‘the Jews should be gassed’, ‘the Jews should be burned’ – we haven’t had that in Germany for decades. Anyone saying those slogans isn’t criticising Israeli politics, it’s just pure hatred against Jews: nothing else. And it’s not just a German phenomenon. It’s an outbreak of hatred against Jews so intense that it’s very clear indeed.”

“It was a historical error to give the Jews their own country in the middle of Islam,” he is quoted as saying. “You’ve had nothing but war ever since and you’ve had anti-Semitism resurging, too. My idea: Give the Jews their own state somewhere in the United States and 25 years to move their state over there.”

Heinsbroek is also quoted as saying that, if implemented, his solution “will finally create, perhaps, peace in the world.”

A record 15,000 French Jews could emigrate to Israel this year amid fears of rising anti-Semitism in Europe, according to the official body overseeing migration to the Jewish state.

The figure – double the number who left France for Israel last year – has been forecast by Natan Sharansky, head of the Jewish Agency, following last Friday’s deadly attack on a kosher supermarket in Paris by a French jihadist, which left four Jewish citizens dead.

The attack prompted an appeal to French Jews by Benjamin Netanyahu, the Israeli prime minister, who told them they would be made welcome if they wished to move to Israel.

Jewish Agency statistics projected that the number of French Jews preparing to make aliyah (emigration) to Israel was on course to reach record levels of around 10,000 even before last week’s attack.